This invention relates generally to membrane separation and, more particularly, to methods for monitoring and/or controlling membrane separation processes.
Membrane separation, which uses a selective membrane, is a fairly recent addition to the industrial separation technology for processing of liquid streams, such as water purification. In membrane separation, constituents of the influent typically pass through the membrane as a result of a driving force(s) in one effluent stream, thus leaving behind some portion of the original constituents in a second stream. Membrane separations commonly used for water purification or other liquid processing include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), electrodialysis, electrodeionization, pervaporation, membrane extraction, membrane distillation, membrane stripping, membrane aeration, and other processes. The driving force of the separation depends on the type of the membrane separation. Pressure-driven membrane filtration, also known as membrane filtration, includes microfiltration, ultrafiltration, nanofiltration and reverse osmosis, and uses pressure as a driving force, whereas the electrical driving force is used in electrodialysis and electrodeionization. Historically, membrane separation processes or systems were not considered cost effective for water treatment due to the adverse impacts that membrane scaling, membrane fouling, membrane degradation and the like had on the efficiency of removing solutes from aqueous water streams. However, advancements in technology have now made membrane separation a more commercially viable technology for treating aqueous feed streams suitable for use in industrial processes.
Further, membrane separation processes have also been made more practical for industrial use, particularly for raw and wastewater purification. This has been achieved through the use of improved diagnostic tools or techniques for evaluating membrane separation performance. The performance of membrane separation, such as efficiency (e.g. flux or membrane permeability) and effectiveness (e.g. rejection or selectivity), are typically affected by various parameters concerning the operating conditions of the process. Therefore, it is desirable to monitor these and other types of process parameters specific to membrane separation to assess the performance of the process and/or the operating conditions. In this regard, a variety of different diagnostic techniques for monitoring membrane separation processes have been routinely used and are now understood and accepted as essential to its practicality and viability for industrial use.
However, monitoring is typically conducted on an intermittent basis, for example, once a work shift or at times less frequently. Known employed monitoring techniques can also be labor and time intensive. Thus, adjustments made to membrane separation processes in order to enhance performance based on typical monitoring may not be made in an expeditious manner. In addition, the presently available monitoring techniques often do not provide optimal sensitivity and selectivity with respect to monitoring a variety of process parameters that are generally relied on as indicators to evaluate and/or control membrane separation processes.
For example, monitoring techniques typically applied to reverse osmosis and nanofiltration include conductivity measurements and flow measurements. Conductivity measurements are inherently less accurate in order to determine the recovery of solutes which are substantially retained by the membrane. In this regard, conductive salts, typically used as an indicator during conductive measurements, can pass through the membrane. Since salts generally pass through the membrane as a percentage of the total salt concentration, changes in local concentration due to concentration gradients or the like can change the conductivity of the product water without necessarily indicating membrane damage. This is especially true in the last stage of a multi-stage cross flow membrane system where salt concentrations (and, therefore, passage of salts as a percentage of that concentration) reach their highest levels. In this regard, the salt passage/percent rejection parameter is generally determined as an average value based on values measured during all stages of the membrane system.
Further, flow meters generally employed in such systems are subject to calibration inaccuracies, thus requiring frequent calibration. Moreover, typical monitoring of reverse osmosis and other membrane separations can routinely require the additional and/or combined use of a number of different techniques, thus increasing the complexity and expense of monitoring.
Accordingly, a need exists to monitor and/or control membrane separation processes which can treat feed streams, such as aqueous feed streams, suitable for use in industrial processes where conventional monitoring techniques are generally complex and/or may lack the sensitivity and selectivity necessary to adequately monitor one or more process parameters specific to membrane separation processes which are important to the evaluation of the performance of membrane separation.
The present invention provides methods and systems for monitoring and/or controlling membrane separation processes capable of treating feed streams suitable for use in industrial processes. In this regard, the detection of inert fluorescent tracers and tagged fluorescent agents is utilized to evaluate and/or control a number of different process parameters unique to membrane separation, such as operational parameters, chemical parameters, a ratio of the inert fluorescent tracer to the tagged fluorescent agent, mechanical parameters and combinations thereof.
The inert fluorescent tracer/tagged fluorescent agent monitoring technique of the present invention can be performed with a high degree of sensitivity and selectivity with respect to the monitoring of process parameters specific to a membrane separation. In this regard, the methods and systems of the present invention can be effectively utilized to optimize the performance of membrane separation processes. Examples of such optimized performance include longer times between membrane cleanings, longer membrane life, verification of treatment chemical in the system, tracking of chemical consumption, ability to operate at optimal recovery, and decreased energy costs due to better control of scaling, fouling and other system parameters.
To this end, in an embodiment of the present invention, a method for monitoring a membrane separation process including a membrane capable of separating a feed stream into a first stream and a second stream to remove solutes from the feed stream is provided. The method includes the steps of providing an inert fluorescent tracer and a tagged fluorescent agent; introducing the inert fluorescent tracer and tagged fluorescent agent into the feed stream; providing a fluorometer to detect the fluorescent signal of the inert fluorescent tracer and the tagged fluorescent agent in at least one of the feed stream, the first stream and the second stream; and using the fluorometer to determine an amount of the inert fluorescent tracer and the tagged fluorescent agent in at least one of the feed stream, the first stream and the second stream.
In another embodiment, a method for monitoring a membrane separation system of a water purification process including a membrane capable of removing solutes from a feed stream suitable for use in an industrial process is provided. The method includes the steps of adding an inert fluorescent tracer and a tagged fluorescent agent to the feed stream; contacting the membrane with the feed stream; separating the feed stream into a permeate stream and a concentrate stream to remove solutes from the feed stream; providing a fluorometer to detect the fluorescent signal of the inert fluorescent tracer and the tagged fluorescent agent in at least one of the feed stream, the permeate stream and the concentrate stream; using the fluorometer to measure an amount of the inert fluorescent tracer and the tagged fluorescent agent in at least one of the feed stream, the permeate stream and the concentrate stream; and determining a ratio of the inert fluorescent tracer to the tagged fluorescent agent based on the measurable amounts of the inert fluorescent tracer and the tagged fluorescent agent.
In yet another embodiment, a membrane separation system capable of purifying a feed stream suitable for use in an industrial process is provided. The membrane separation system includes a semi-permeable membrane capable of separating the feed stream containing an inert fluorescent tracer and a tagged fluorescent agent into a permeate stream and a concentrate stream to remove one or more solutes from the feed stream; a detection device capable of fluorometrically measuring an amount of the inert fluorescent tracer and the tagged fluorescent agent each ranging from about 5 parts per trillion (xe2x80x9cpptxe2x80x9d) to about 1000 parts per million (xe2x80x9cppmxe2x80x9d) in at least one of the feed stream, the permeate stream and the concentrate stream wherein the detection device is capable of producing a signal indicative of the amount of inert fluorescent tracer and tagged fluorescent agent that is measured; and a controller capable of processing the signal to monitor and/or control the purification of the feed stream. Such monitoring or control may include control of chemical dosing and checking the accuracy/calibration of standard instruments (e.g. flow sensors).
In still another embodiment, a method for monitoring and controlling a membrane separation process including a membrane capable of removing solutes from a feed stream for use in an industrial process is provided. The method includes the steps of adding an inert fluorescent tracer and a tagged fluorescent agent to the feed stream; contacting the membrane with the feed stream; separating the feed stream into a first effluent stream and a second effluent stream to remove solutes from the feed stream; providing a fluorometer to detect the fluorescent signal of the inert fluorescent tracer and the tagged fluorescent agent in at least one of the feed stream, the first effluent stream and the second effluent stream; using the fluorometer to measure the inert fluorescent tracer and the tagged fluorescent agent in an amount ranging from about 5 ppt to about 1000 ppm in at least one of the feed stream, the first effluent stream and the second effluent stream; and evaluating at least one process parameter specific to membrane separation based on the measurable amounts of the inert fluorescent tracer and the tagged fluorescent agent.
It is, therefore, an advantage of the present invention to provide methods and systems that utilize inert fluorescent tracers in combination with tagged fluorescent agents to monitor and/or control membrane separation processes or systems.
Another advantage of the present invention is to provide methods and systems that utilize measurable amounts of inert fluorescent tracers and tagged fluorescent agents to improve the operational efficiency of membrane separation processes or systems.
A further advantage of the present invention is to provide methods and systems for monitoring parameters specific to membrane separation processes with selectivity, specificity and accuracy based on measurable amounts of inert fluorescent tracers and tagged fluorescent agents added to the membrane separation system.
Yet another advantage of the present invention is to provide methods and systems for monitoring and/or controlling membrane separation processes for purifying aqueous feed streams suitable for use in industrial water systems.
Still further an advantage of the present invention is to enhance performance of membrane separation processes or systems that utilize cross-flow and/or dead-end flow separation to remove solutes from feed streams.
Additional features and advantages of the present invention are described in, and will be apparent in, the detailed description of the presently preferred embodiments.